The second seed recovered from a third-set wobble to claim a 7-5 6-2 3-6 6-3 victory.

Czech Mensik, 20, beat 19-year-old Fonseca 6-4 6-3 7-6 (3) on Court Philippe Chatrier.

The 20-year-old Czech needed attention from medical staff before being taken to the locker room in a wheelchair.